The present invention relates to one part heat curable organopolysiloxane compositions resulting from a platinum catalyzed addition cure of an olefinically unsaturated organopolysiloxane and organohydrogenpolysiloxane. More particularly the present relates to the use of a microencapsulated platinum catalyst in a one part heat curable organopolysiloxane mixture.
Prior to the present invention, a one part heat curable organopolysiloxane compositions based on the use of a platinum catalyst to effect addition between a silicon hydride and an olefinically unsaturated organopolysiloxane was shown by Imai, U.S. Pat. No. 4,293,677. Although valuable results are achieved by Imai's method, encapsulation of the organohydrogenpolysiloxane, is required. Accordingly, large amounts of an incompatible encapsulating material are required to achieve effective results. The physical properties and optical characteristics of the cured material are often adversely affected.
Schlak et al, U.S. Pat. No. 4,481,341 is directed to a one package heat curable thermosetting organopolysiloxane composition utilizing a platinum catalyst in an organopolysiloxane having at least two olefinically unsaturated hydrocarbon groups attached to silicon, and an organohydrogenpolysiloxane. The platinum catalyst in Schlak's composition is dispersed in bulk in a solid substance such as a silicone resin or polyester resin having a softening point between about 70.degree. C. to 250.degree. C. The platinum containing mass has to be ground prior to its use in the organopolysiloxane mixture. Again, the bulk encapsulant for the platinum catalyst is insoluble in the organopolysiloxane mixture. As a result, the appearance of the cured product also can be adversely affected. In addition, the shelf life of the organopolysiloxane is sometimes unsatisfactory, as the platinum catalyst can be exposed when the bulk encapsulated platinum is ground prior to its incorporation into the one part heat curable organopolysiloxane mixture.
Various procedures have been developed utilizing thermosetting material, such as phenolics, and melamine formaldehyde reaction products, to manufacture minute capsules for encapsulating a variety of materials for different purposes. For example, Hart et al, U.S. Pat. No. 3,755,190 is directed to an encapsulation process using an in-situ polymerization reaction of polyhydroxy phenolic materials with aldehyde materials. Some of the materials which are encapsulated by the aforementioned technique, are water insolubles, inert to the encapsulating materials, such as various oils, for example, olive oil, fish oils, mineral oil, xylene and similar materials. Further improvements in capsule manufacture is shown by Hayford U.S. Pat. No. 4,444,699. A polymerization reaction is effected between melamine and formaldehyde and/or the polycondensation of methylol, or etherified methylol melamine, monomeric methylolmelamine, or etherified methylol melamine, or a low molecular weight polymer thereof. Materials which are encapsulated include a mixture of chromogeneric compounds, such as of 3,3-bis(p-dimethylaminophenol)-6-dimethylaminophthalide), mixed with other materials and dissolved in a mixture of C.sub.10 -C.sub.13 alkyl benzene and benzylated xylenes.